Electrophotographic photosensitive members generally include supports and photosensitive layers disposed on the supports. Some of the photosensitive layers are a lamination type including a charge-generating layer containing a charge-generating material and a charge-transporting layer containing a charge-transporting material.
In general, the charge-transporting layer is formed as a uniform layer by a method where a coating film is formed by application of a coating liquid prepared by dissolving a low-molecular-weight charge-transporting compound serving as a charge-transporting material and a resin (binder resin) serving as a binder material in a solvent and drying the resulting coating.
Meanwhile, PTLs 1 and 2 disclose techniques of providing ununiform charge-transporting layers in order to obtain high-gamma electrophotographic photosensitive members, reduce residual potentials, and maintain high image qualities for a long time. In each method of forming a ununiform charge-transporting layer disclosed in PTLs 1 and 2, a coating film is formed by application of a dispersion solution prepared by dispersing charge-transporting pigment particles in a solution (polymer solution) in which a polymer is dissolved in a solvent and drying the resulting coating.
Unfortunately, in the case of using the dispersion solution prepared by dispersing charge-transporting pigment particles in a polymer solution, insufficient dispersion treatment of the charge-transporting pigment particles, low solution stability of the prepared dispersion solution, or occurrence of aggregation of the charge-transporting pigment particles during drying of the coating may be caused. Consequently, a deviation in charge transfer in the charge-transporting layer, an insufficient sensitivity of the electrophotographic photosensitive member, or an insufficient reduction of the residual potential may occur.
PTL 3 discloses a method of forming an intermediate layer of an electrophotographic photosensitive member using a dispersion solution prepared by dispersing charge-transporting pigment particles (electron-transporting pigment particles) in a polymer emulsion.